The Purification and Characterization of Three Protease Inhibitors, Alpha 1 Antitrypsin (Alpha 1 AT), Antithrombin III (AT III) and alpha 2 Macroglobulin (alpha 2 MG), of Human Plasma. Investigations on the interactions of alpha 1 antitrypsin, antithrombin III and alpha 2 macroglobulin with trypsin and chymotrypsin will be continued and extended to include the interaction of the inhibitors with thrombin. Purification of human thrombin and certain other components of the coagulate cascade will be undertaken and then interaction with the inhibitors will also be investigated. It is hoped that these in vitro measurements will assist in the delineation of the role of the inhibitors and proteases in vivo. Studies on the Surface Behavior of Plasma Lipoproteins and Model Macromolecules. The direct determination of surface excess concentration as a function of time and solute concentration will be determined by the radioactive tracer method, using bovine and human serum albumin, human HLD(alpha)-lipoprotein, human LDL (beta)-lipoprotein, and other model macromolecules. The lipoproteins will be labelled (in separate experiments) in both the apoprotein and lipid moieties. These direct determinations will be compared with surface excess concentrations calculated from the Gibbs adsorption isotherm, using dynamic surface tension studies. The aim of these studies is to determine the surface configuration of the protein solutes, especially in the case of the lipoproteins of plasma.